The Hebgen Lake, Montana, earthquake of August 18, 1959: P waves

1962 ◽  
Vol 52 (2) ◽  
pp. 235-271
Author(s):  
Alan Ryall
Keyword(s):  
Travel Time ◽  
Sierra Nevada ◽  
Fault Plane ◽  
Time Curve ◽  
P Waves ◽  
Arrival Times ◽  
The Pacific ◽  
First Motion ◽  
Plane Solution ◽  
The Pacific Ocean

ABSTRACT The instrumental epicenter of the Hebgen Lake earthquake is found to lie within the region of surface faulting. The depth of focus had a maximum value of 25 kilometers. Times of P are studied in detail for epicentral distances less than 13 degrees. The apparent scatter of arrival times from 700 to 1400 kilometers can be explained by variations of the velocity of Pn between the physiographic provinces of the western United States. A comparison of observations for the Hebgen Lake earthquake with published times for blasts in Nevada and Utah indicates that the velocity of Pn in the central and eastern Basin and Range is about 7.5 km/sec, and that the crust in that region thickens toward the east and thins toward the south. A comparison of apparent velocities in northern California, in directions parallel and transverse to the structure, indicates that the crust thins by about 19 kilometers, from the edge of the Sierra Nevada to the Pacific Ocean. A discontinuity is observed in the travel-time curve at a distance of 24–25 degrees. Arrivals of P waves in the range 65–128 degrees fall on two parallel travel-time branches; this multiplicity in the travel-time curve may be related to repeated motion at the source. Travel-times of PKIKP appear to deviate from published curves. The fault-plane solution for the Hebgen Lake earthquake, together with a consideration of the first motion at Bozeman, Montana, indicates a focal mechanism of the dipole, or fault, type. The strike and dip of the instrumental fault plane agree well with observed ruptures at the surface.

Spatial distribution and source mechanism of microearthquakes in Central Nevada

1967 ◽  
Vol 57 (6) ◽  
pp. 1317-1345 ◽  
Author(s):  
William Stauder ◽  
Alan Ryall
Keyword(s):  
Fault Plane ◽  
Time History ◽  
Surface Velocity ◽  
Time Intervals ◽  
Surface Fracture ◽  
Arrival Times ◽  
Propagation Effects ◽  
First Motion ◽  
Plane Solution ◽  
Southern Extremity

Abstract During the summer of 1966 a small tripartite array was established at the southern extremity of the surface faulting of the Fairview Peak earthquake of 1954. Over a period of six weeks an average 31 earthquakes per day were detected. Of these approximately 400 were selected for detailed study. Site corrections were made to reduce arrival times for all elements of the array to a common base, and the properties of the array and S-P time intervals were used to determine direction of approach, apparent surface velocity across the array, and hypocentral coordinates. Foci were found to concentrate at a depth of 10 to 15 kilometers and to cluster toward the end of the surface faulting of the 1954 earthquake. The foci were also found to lie along two planar zones. The first is parallel to the fault plane solution (strike N 11° W, dip 62° E) of the Fairview Peak earthquake and terminates at the southern extremity of the surface fracture. The second begins at this point and extends to the southwest, with foci distributed about a plane striking N 50° E and dipping 50° to the southeast. The latter zone apparently marks the southern terminus of the 1954 faulting. The polarity of the first motion of P at the array indicates predominantly dip-slip motion along the faults of both zones. The character of the seismic signatures from foci occurring closely together in space and time indicates that the complexity of the signature arises chiefly from propagation effects rather than from complexity of the time history at the source.

The Texas earthquake of August 16, 1931*

1934 ◽  
Vol 24 (2) ◽  
pp. 81-99
Author(s):  
Perry Byerly
Keyword(s):  
Travel Time ◽  
Travel Times ◽  
Time Curve ◽  
P Waves ◽  
First Order ◽  
First Motion ◽  
Order Discontinuity

Summary The travel-time curve of P for the Texas earthquake of August 16, 1931, shows that there is a definite break in the travel-time curve near Δ = 16°. This is interpreted as indicating a first-order discontinuity at a depth of about 300 kilometers. Another break in the travel-time curve at Δ = 25° is strongly suggested. Beyond Δ = 75° the curve has two branches, the lower following most existing curves, the upper following the Montana curve which latter seems to be a usual one for American earthquakes. This part of the curve is interpreted as indicating that the discontinuity at depth about 2,400 kilometers is a first-order one at which the speed of P waves drops discontinuously. From the direction of first motion on the records it is concluded that a sufficient source would have been motion on a fault of strike about N 35° W, the movement being up on the easterly side and down on the westerly side. The travel times of all waves read on the records are plotted on graphs. The scattering of all waves after P is marked.

The Alaskan earthquake of July 22, 1937*

1940 ◽  
Vol 30 (4) ◽  
pp. 353-376
Author(s):  
John N. Adkins
Keyword(s):  
Travel Time ◽  
Epicentral Distance ◽  
Time Interval ◽  
Time Curve ◽  
Arrival Times ◽  
The Earth ◽  
Geographical Latitude ◽  
The World ◽  
First Motion ◽  
First Arrival

Summary The study of the Alaskan earthquake of July 22, 1937, is based on the examination of original seismograms and photographic copies from seismological observatories throughout the world. The arrival times of P at 71 stations were used in locating the epicenter. By Geiger's method and the use of Jeffreys' travel times, the position of the epicenter was found to be: geographical latitude, 64.67±.04° N, longitude, 146.58±.12° W, and the time of occurrence to be 17h 9m 30.0±.25s, U.T. The epicenter lies in the Yukon-Tanana upland in central Alaska, which is not a region of frequent major earthquakes. The disagreement caused by the apparently early arrivals at College and Sitka was reduced by replacing the standard travel-time curve of P by a linear travel-time curve in the interval of epicentral distance 0° to 16° and by interpreting the first arrival at College as P. It was possible to determine the direction of the first motion of P for 51 stations. The observed distribution of first motion and the geological trends in the region of the epicenter are consistent with the earthquake's having been caused by movement along a fault with strike between N 30° E and N 37° E, and dip between 64° and 71° to the southeast, in which the southeast side of the fault was displaced relatively northeastward with the line of movement pitching between 12° and 16° northeast. A wave designated F (for “false S”) was found to precede S on the records by 20 to 55 seconds, depending on the epicentral distance. The wave is longitudinal in type and the arrival times define a linear travel-time curve. It is suggested that this wave may be a longitudinal surface wave, of the type proposed by Nakano, produced at the surface of the earth by the arrival of a transverse wave which has been reflected at a surface of discontinuity within the earth. The records show two impulses near the time when S is expected. The average time interval between the two impulses is 11.3 sec. The first, called S1, has a plane of vibration intermediate in direction between the plane of propagation and the normal thereto. The second impulse, called S2, is nearly pure SH movement. The writer wishes to express his indebtedness to Professor Perry Byerly for invaluable suggestions and criticism during the course of the investigation.

Near earthquakes in Central California*

1939 ◽  
Vol 29 (3) ◽  
pp. 427-462 ◽  
Author(s):  
Perry Byerly
Keyword(s):  
Least Squares ◽  
Travel Time ◽  
Sierra Nevada ◽  
Accurate Determination ◽  
Depth Of Focus ◽  
Surface Layers ◽  
P Waves ◽  
Central California ◽  
The Waves

Summary Least-squares adjustments of observations of waves of the P groups at central and southern California stations are used to obtain the speeds of various waves. Only observations made to tenths of a second are used. It is assumed that the waves have a common velocity for all earthquakes. But the time intercepts of the travel-time curves are allowed to be different for different shocks. The speed of P̄ is found to be 5.61 km/sec.±0.05. The speed for S̄ (founded on fewer data) is 3.26 km/sec. ± 0.09. There are slight differences in the epicenters located by the use of P̄ and S̄ which may or may not be significant. It is suggested that P̄ and S̄ may be released from different foci. The speed of Pn, the wave in the top of the mantle, is 8.02 km/sec. ± 0.05. Intermediate P waves of speeds 6.72 km/sec. ± 0.02 and 7.24 km/sec. ± 0.04 are observed. Only the former has a time intercept which allows a consistent computation of structure when considered a layer wave. For the Berkeley earthquake of March 8, 1937, the accurate determination of depth of focus was possible. This enabled a determination of layering of the earth's crust. The result was about 9 km. of granite over 23 km. of a medium of speed 6.72 km/sec. Underneath these two layers is the mantle of speed 8.02 km/sec. The data from other shocks centering south of Berkeley would not fit this structure, but an assumption of the thickening of the granite southerly brought all into agreement. The earthquakes discussed show a lag of Pn as it passes under the Sierra Nevada. This has been observed before. A reconsideration of the Pn data of the Nevada earthquake of December 20, 1932, together with the data mentioned above, leads to the conclusion that the root of the mountain mass projects into the mantle beneath the surface layers by an amount between 6 and 41 km.

Earthquake/earth tide correlation and other features of the Susanville, California, earthquake sequence of June-July 1976

1980 ◽  
Vol 70 (5) ◽  
pp. 1583-1593
Author(s):  
Amy S. Mohler
Keyword(s):  
Shear Stress ◽  
Compressive Stress ◽  
Sierra Nevada ◽  
Fault Plane ◽  
Earth Tide ◽  
P Wave ◽  
First Motion ◽  
Entire Sequence ◽  
June July ◽  
Earthquake Sequences

abstract An earthquake of magnitude ML 4.5 occurred on June 20, 1976 in an area of complex faulting in northeastern California, near the intersection of the Sierra Nevada, Modoc Plateau, Cascade Range, and Basin and Range geological provinces. P-wave first motion plots for larger aftershocks of this earthquake indicate maximum and minimum compressive stress, respectively, in north-south and east-west directions, with predominantly strike-slip motion. Focal depths for these events ranged from 7 to 15 km, consistent with other earthquake sequences in the region. Origin times of more than 4,700 aftershocks for the period between June 20 and July 1 are compared with the phase of solid-earth tidal components appropriate for normal and shear stress on northeast- and northwest-trending fault planes. Based on this comparison, approximately 20 per cent more earthquakes occurred at times when the normal compressive stress on the fault plane was decreasing, and the shear stress was increasing in the sense of slip on the fault plane. This correlation may be explained by two large bursts of aftershocks that occurred at times when tidal stresses were favorable for motion on the fault plane, rather than continuous triggering of small events during the entire sequence.

The Peru-Bolivia border earthquake of August 15, 1963

1970 ◽  
Vol 60 (2) ◽  
pp. 639-646 ◽  
Author(s):  
Umesh Chandra
Keyword(s):  
Travel Time ◽  
Fault Plane ◽  
P Wave ◽  
Focal Mechanism Solution ◽  
Event Analysis ◽  
Rupture Propagation ◽  
Fault Propagation ◽  
Amplitude Data ◽  
First Motion ◽  
Deep Focus

abstract The seismograms of the deep focus Peru-Bolivia border earthquake of August 15, 1963 reveal the presence of a number of conspicuous phases occurring within 15 seconds of the first P onset. These phases cannot be explained on the basis of known travel-time curves. Accordingly, the earthquake is interpreted to have occurred in a series of jerks during the course of fault propagation, or in other words it is composed of multiple events. Only one of these events, following the first event, at which the amplitude of the recorded motion becomes suddenly very large, has been located in this study. The focal mechanism solution of this earthquake has been determined from the P wave first motion and amplitude data. Consideration of the direction of rupture propagation determined from the multiple event analysis makes it possible to identify the fault plane in the mechanism solution. The parameters of the fault plane, length and speed of rupture between the two events have been determined.

How Weird Squiggles Led from Sheaves of Rice to the Depth of the Seas

Tsunami ◽  
2021 ◽  
pp. 17-26
Author(s):  
James Goff ◽  
Walter Dudley
Keyword(s):  
Pacific Ocean ◽  
Travel Time ◽  
San Francisco ◽  
Geodetic Survey ◽  
Government Agencies ◽  
Tidal Waves ◽  
Earthquake Detection ◽  
The Pacific ◽  
The Pacific Ocean ◽  
1946 Tsunami

Through an amazing chain of events, the Japanese story of how a town squire sacrificed his wealth to save his villagers from a deadly tsunami is intricately woven together with how in 1855 Benjamin Franklin’s great grandson accurately determined the depth of the Pacific Ocean based on the travel time of this same tsunami from Japan to San Francisco, California. This scientific breakthrough would lead to the first known prediction of tsunami wave generation through earthquake detection yet would be ignored by official government agencies with tragic consequences. Immediately following the 1946 tsunami, the Commander of the Coast and Geodetic Survey ignorantly stated, “Less than one in one hundred earthquakes result in tidal waves and you don’t alert every port in the Pacific each time a quake occurs.”

Fault-plane solution for the Tango, Japan, earthquake of March 7, 1927*

1955 ◽  
Vol 45 (1) ◽  
pp. 37-41
Author(s):  
John H. Hodgson
Keyword(s):  
Fault Plane ◽  
Independent Solution ◽  
Relative Displacement ◽  
Fault Plane Solution ◽  
First Motion ◽  
Plane Solution

Abstract In an attempt to obtain confirmation of the fault-plane methods in use by the Dominion Observatory by comparison with an observed fault, a solution has been attempted for the Tango, Japan, earthquake of March 7, 1927. The direction of first motion was read from seismograms, accumulated for an earlier study by E. A. Hodgson, and filed at Ottawa. The data derived from the records are not sufficient to allow an independent solution that is very closely defined, but it is shown that they do satisfy the known strike, dip, and relative displacement very well.

A P Travel-Time Model for the Canadian Shield obtained by a Joint Epicenter Determination Method

1974 ◽  
Vol 11 (5) ◽  
pp. 611-618 ◽  
Author(s):  
M. Hashizume
Keyword(s):  
Travel Time ◽  
Canadian Shield ◽  
Time Model ◽  
Time Curve ◽  
Origin Time ◽  
Arrival Times ◽  
Shallow Earthquakes ◽  
Starting Point ◽  
Order Polynomial

The P arrival-times for nine very shallow earthquakes under the Canadian Shield and the surrounding area were studied. P arrival-times were assumed to be a function of the hypocenter, origin-time, and specified travel-time curve. Using as starting point the hypocenters and origin times taken from the Preliminary Determination of Epicenters (PDE) listings and the travel-time curve from the "Seismological Tables for P Phases" by Herrin et al. (1968), calculations were conducted so as to minimize the residuals between the observed P arrival-times and the calculated travel-times in a search for the best hypocenters, origin-times, and travel-time curve. The deviations from the travel-time curve were assumed to be represented by a sixth-order polynomial. The differences of the new epicenters from those of the PDE listings are small and generally less than about 10 km. The significant result is that the new travel-time curve obtained by this technique is similar to those obtained from seismic explosion studies in the eastern part of North America.

scholarly journals On supposed discontinuities in the mantle of the Earth

1931 ◽  
Vol 21 (3) ◽  
pp. 216-223 ◽  
Author(s):  
B. Gutenberg ◽  
C. F. Richter
Keyword(s):  
Travel Time ◽  
Glassy State ◽  
Time Curve ◽  
P Waves ◽  
S Waves ◽  
The Earth ◽  
Straight Line

Summary Investigations of the Mexican shocks of January 2, 15, and 17, 1931, as recorded at stations in California have shown that the travel-time curve of the P-waves at distances between 9° and 15° is nearly a straight line. At these distances the amplitudes of the P-waves are very small, as is to be expected from theory. At greater distances dt/dΔ decreases, and the amplitudes are larger. The data are not sufficient to decide whether the changes are abrupt or not. No S-waves could be found between 9° and 15°. The calculated velocities of the P-waves are near 8.2 kilometers per second at depths between 40 and 100 kilometers, increasing slightly with greater depths. It is possible that the velocity decreases very slightly at some depths between 40 and 80 kilometers, but there is no sign of any discontinuity at depths between 40 and more than 500 kilometers. The S-waves seem to be affected a little more at depths between 40 and 100 kilometers than the P-waves. It is not impossible that at some depth between 40 and 80 kilometers there is a transition from the crystalline to the glassy state.

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